Vista Bug - Misinterpretation of Logical Partitions

The illustrations below are screen captures from XP's Disk Management and Vista's Disk Management screens. The disk has 8 partitions--three primaries plus an extended partition containing 5 logical volumes. In each illustration, the partitions themselves have not been altered in any way, only the 'partition-type' code in the partition table descriptors have been changed. The 'partition-type' codes are overlaid in red below each partition. The following partition types are represented:



The first illustration (above) is from XP's Disk Management. The system is booted from the 4th partition--the first logical. Three alternate OS's are in hidden NTFS partitions. Three data partitions are visible at the end of the extended partition. Note that XP gets it right--there are 5 partitions inside the extended partition.





The second illustration (above) is the exact same disk as seen from Vista's Disk Management, except it is now booted from the third partition. There are still 5 partitions in the extended partition, but note Vista misinterprets the first two as Primary Partitions, even though it's not possible to have 5 primary partitions in the partition table! Remember, no partition boundaries have been altered, and the extended partition is still the same size. Only the partition-type code in the partition table descriptors (shown in red) have been changed.





The third illustration (above) is the same disk as seen from Vista again, except I have deliberately changed the partition-type codes of the last two partitions to 'DD' and '83'. Remember, I have not altered the partition, I have only changed the partition table descriptor. This is exactly what Dell does with their MediaDirect (v3) partition--it is an ordinary NTFS partition with the partition table descriptor changed. There are still 5 volumes in the extended partition, but Vista misinterprets this disk as having an impossible 7 primary partitions!

Note that I included '83' just to show this Vista bug is not unique to Dells. Anyone who has a Vista/linux dualboot system with linux partitions in the extended partition will notice the same phenomenon.

This Vista bug causes much confusion among people with Dell laptops as to their partition layout. Dell's Vista laptops come from the factory with: If you want to create a data partition, shrink the back end of the "OS" partition, move the newly unallocated space inside the extended partition (ie, extend the front edge of the extended partition), then create a new logical volume out of this unallocated space. You will now have 3 primaries plus an extended partition containing two logical volumes. (Note: the new volume will be in front of the MediaDirect partition.)

But you have to use a reliable tool. Vista's Disk Management cannot do this because it misinterprets the MediaDirect partition as a fourth primary partition, so while it can shrink the "OS" partition, it cannot create a new partition out of the freed up space because it mistakenly thinks you already have four primaries.



Dan Goodell
06/25/2009

(2015 update: This bug still exists in Windows 7, 8.x and 10.)